Medical Electronics 1

7/28/2019 Medical Electronics 1

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ASL PAULS COLLEGE OFENGINEERING AND TECHNOLOGY

MEDICAL ELECTRONICS

Prepared by,

S.Rameshprabhu M.E., (PhD)

Asst professor EEE Dept



UNIT-1

Recording andmonitoring

instruments



Bio Electric SignalIn 18th century Galvani demonstrated that most

of the physiological process were accompaniedwith electrical changes.

From this discovery the action of living tissueare explained in the terms of Bio electricpotentials.

The human body consist of living tissues and itis considered as power station generatingmultiple electrical signal with two internalsources namely muscles and nerves.

The bio electric signal are the signal generatedby nerve cells and muscle cells. The electricfield generated by the action af many cellconstitutes Bio electric signal.

Eg : ECG,EEG,EMG,etc…..



BIOELECTRIC POTENTIALS:

Bioelectric potential are generated at a cellularlevel.

Each cell is a minute voltage generator, because+ve and –ve ions tends to concentrate unequallyinside and outside the cell wall.

Therefore the potential difference(resting

potential) is established and the human cell actsas tiny biological battery.

Their basic source is cell membranepotential(resting potential) which certain

condition may be excited to generated an actionpotential.

The discharging and recharging of the cell istermed as depolarization and repolarization

respectively



Relationship between action potential andmuscle contraction:



Potential

The diffusion and drift process give rise to

balance of ions between inside and outside of thecell.

Generally the nerve cells readily permit the entryof potassium and chloride ions. But it blocks the

entry of sodium ions. The equilibrium condition is reached with the

potential difference across the membrane, suchthat negative potential on inside and positivepotential on the outside. The membrane potentialcaused by different concentration of ions is calledResting Potential. When human cell is inresting stage, it is said to be polarized.



Characteristics of Resting Potential:

The value of the resting potential ismaintained as a constant until some kind of the disturbance will upset the equilibrium.

It strongly depend upon the temperature.

The range(VR) of resting potential is -60mV to

-100mV.VR is derived from Goldman's equation,

Where,

o and i – outside and inside the cell.VR – resting potential, k – Boltzman constant,

T – Absolute temperature in Kelvin.

q – charge of electron, PK - permeability of

potassium ion.



According to Goldman’s equation resting potential.

VR=-86.8mV

According to nertz equation

PNA & PCL ≈

0VR=- 94.9mV

ACTION POTENTIAL:

When the cell membrane is excited by some

energy, then the permeability changes. So thatthe sodium ions are allowed to enter inside thecell. So the cell has +ve potential inside due toimbalance of potassium ions.

The positive potential of cell membrane duringexcitation is called Action potential. Therange(VR) of Action potential is 20mV.



As long as the action potential exist the cell is saidto be “Depolarized state”.

After sometime, when the passage of sodium ions is

stopped, the cell membrane reversed back to theoriginal condition is called “Repolarization state”.

There are many Bio electric signal present in our ownhuman body. They are ,

ECG(Electro Cardiogram)- Electrical activity of heartEEG(Electro Encephalogram)-Neuron of brain

ERG(Electro Rectinogram) – Eye

EMG(Electro Myogram)- Muscle contraction





ELECTRODES:Electrode are generally used to pickup electrical

signals from the body.

The voltage developed at an electrode-electrolyte(body fluid) interface is termed as half cell potential or Electrode potential. The half cellpotential are obtained using surface electrode.

Perfectly Polarized Electrode:No net transfer of charge occurs at the metal

electrolyte interface.

Perfectly Non Polarisable Electrode:

Infinite exchange of charge occurs, across themetal electrolyte.

Some of the electrode are:

Surface electrode- potential across skin surface.

Micro electrode- potential near or within single cell.



Recording Electrode:

Bio electric events have to be pick up from thesurface of the body before they can be put into the

amplifier for subsequent record or display. This isdone using electrode.

They are two types

Practice surface electrode (on the tissue without

damaging living tissue)Deep seated electrode(Inside the living tissue or

cell)

Electrode used for ECG:

Limb electrodeFloating electrode

Pre gelled disposable electrode

Pasteless electrode



Limb electrode :

Used in forelimbs of body

The material used is German silver , nickel silver. They are applied to the surface of the body withelectrode jelly. The electrode jelly forms vacuumseal.

The impedance of this electrode is 2 to 5kΩ.Measured at 10 Hz and size is 3X5 cm.



Floating electrode:

Light weight floating electrode with press stud forlong term monitoring of ECG.

No jelly is used, impedance of this electrode is 50kΩ.



Pre gelled Disposable Electrode:

Electrode which are employed in stress testing andlong term monitoring.

Gel contains electrolyte paste withbactericide/fungicide.

Cause minimum skin irritation where this gel haspH range 3.5-9.

Problems under stress can be detected using thiselectrode.



Pasteless electrode:

It is Dry electrode i.e contains no paste. Free fromproblems reg gel.

Draw back are it has high skin resistance and strongsensitivity to motion. Hence it can be overcome byusing high value of amplifier input resistance.

It has shell, 2 FET , can of diameter 4.5mm and op-

amp of high AC impedance(> 100MΩ).



Electrodes for EEG:

Among the commonly used electrode for EEGrecording are the chloride silver discs having

approximately 6-8mm diameters.Contact with the scalp via electrolytic paste through

a washer of soft felt. They have resistance varyingfrom 3-20kΩ.

Small needle electrode are sometimes used forcarrying out special EEG studies when they areinserted subcutaneously.

Pad electrode is used in EEG.



Electrodes for EMG:

Electrode for EMG work are usually of the needletype.

This electrode are used in neurography and otherelectrophysiological investigations of the muscletissues under the skin and in deeper tissues and torecord nerve action potential.

The material of needle electrode is generally of stainless steel. Needle electrode are designed to befully autoclavable and in any case they should bethoroughly sterilized before use.

They are of various forms

Monopolar – one reference electrode are used.

Bipolar – one is reference and other is active.



Hypodermic needle type EMG electrode are specialtype where active and reference electrode are usedin same needle.



Microelectrode:

To measure the electrical activity of single cell.

Very thin electrode so that the penetration by

the electrode does not damage the cell. It islocated within the cell, where the referenceelectrode are placed outside the cell.

The metal microelectrodes are formed by

electrolytically etching the tip of fine tungstenfilament or simple stainless wire.

The potential within the cell can be measured byusing 2 electrode.Microelectrode.

Reference electrode.

Microelectrode are broadly classified intoMetallic electrode (Metal electrolyte)

Micropipet( instead of metal electrolyte non





Chemical Electrode:

Various type of chemical electrode are,Hydrogen electrode It is used as standard reference electrode. It is used to

measure the pH of body fluid.

During the measurement of potential, the hydrogen gasshould be supplied. This measurement is not stable onetherefore, it should not act as reference electrode. Hence

we go for practical reference electrode.Practical electrode(Silver –silver chloride is

used as ref electrode)

pH electrode:

The chemical balance of the human body is identified bythe measurement of pH content of the blood and otherbody fluids.

To measure hydrogen ion concentration. The pH is givenby,

pH= - log [H+]Normally pH of blood is slightly greater than 7.



pH electrode:



pCO2 electrode:

It consist of standard glass pH electrode covered with therubber permeable membrane. Between the glass surface andmembrane there is a thin film of water.

The solution under the test which contains a dissolved CO2 ispresented to the outer surface of the rubber membrane.

pO2 electrode:

The oxygen electrolyte consist of a piece of platinum wireembedded in an insulating glass holder.

The electrode is exposed to the electrolyte into which oxygenfrom the solution under measurement is allowed to diffusethrough the membrane.

The reduction of O2 is takes place in platinum and currentdeveloped is proportional to the partial pressure of diffused

oxygen.



Biomedical Recorders

Biomedical recorder are used record the

biomedical signals like ECG, EEG, EMG,etc….

Electrocardiography[ECG]:

Electrocardiograph shows the electrical activityof heart muscle.

It gives information about cardiac disorder.

The recorded ECG waveform is calledeletyctrocardiograph and instrument used to

record is called electrocardiogram.ECG lead system:

The types of lead system areBipolar lead system(standard lead system)

Unipolar lead system (Augmented unipolar limb



Bipolar lead system:

In this lead system ECG is recorded by using 2electrode.

The final output(electrical potential) is takenbetween these 2 electrode.

It is called Einthoven leads.

In this system electrodes are placed in 4different places,LA(left arm)LL(left leg)

RA(Right Arm)RL(Right Leg)



Lead I position: It gives voltage drop V1 from LAto RA.

Lead II position: It gives voltage drop V2 from

LL to RA.Lead I position: It gives voltage drop V1 from LA

to LA.



The closed path from RA to LA to LL called Einthoventriangle.

V1=0.53mV, V2=0.71mV, V3=0.38mV

Always V2=V1+V3(Kirchoff Law is followed)



Augumented Unipolar Limb leads:

This system is introduced by Wilson, the voltageis taken between single exploratory electrodeand central terminal.

Two equal resistor are connected to a pair of limb electrode and the center point act as oneterminal to measure voltage.

In this lead system, small increase in the ECGvoltage can be realized. 3 Augumented leadconnection are possible, they are Augumented Voltage Right Arm(aVR)

Augumented Voltage Left Arm(aVL)

Augumented Voltage foot(aVF)



Lead avL Lead avR

Lead avF



ECG Recording Method



Lead Selector:

The potential picked up by the patientelectrode are taken to the lead selector

switch. The electrode are selected two by twoaccording to lead program.

Preamplifier:

It has 3 or 4 stage differential amplifier, which

give stabilizing effect.It has high gain and CMRR.

It prevents the patient from electrical shockand over voltage protection.

Power amplifier:

The amplified signal is picked up by the poweramplifier

It is used to drive output unit. The pen motor



Feedback Network:

It consist of RC circuit. It provides necessarydamping to the pen motor.

Auxiliary circuit:

It provided 1mV calibration signal.

The automatic blocking is provided when

change in position of lead switch. It includespeed control circuit of chart drive motor.

Output Display unit:

CRO or paper chart recorder is used as output

unit.Pen motor is used in output.Paper speed- 25mm/s in US manufacturing

system.

Paper speed - 50mm/s in European ECG.



Analysis of ECG Waveform:

Fig (b) shows first degree AV block. PQ is prolongedcond time(>0.22s)

(c) shows Widening of QRS complex.(QRS period>0.1s).

(d) shows elevation in ST. results Myocardinalinfarction.

(e) shows negative T wave. It results in Coronaryinsufficiency.

(f) shows completely different ECGwaveform trian ular . It is due to ventricular



Electroencephalography(EEG):

It is the study of electrical activity of the brain. Thebiological name of brain in encephalon.

Electrodes are placed on the scalp.Monitoring EEG has proven to be effective method

of diagnosing many neurological illness and diseaseas epilepsy, tumor and problems associated with

trauma.Unlike ECG, the EEG measurement is made for

longer time.

Action Potential of the brain:



Action Potential of the brain:

The resting potential along with a nerve fiberis used to transmit the information from end toanother.

Inhibitory post synaptic potential(IPSP)If the transmitter substance is inhibitory, then

the membrane potential of the receptor neuronincreases in a negative direction. So it is lesslikely to discharge. The induced potential changeis called IPSP.

• Excitatory Post Synaptic Potential(EPSP) If the transmitter substance is excitatory, then

the membrane potential of the receptor neuronincreases in a positive direction. So it is morelikely to discharge and produce spike potential.

The induced potential change is called EPSP.

• Evoked Potential:



Placement of electrode in EEG measurement:

• Anterior-Posterior Measurement(10 -20electrode system)

The distance between 2 electrode is 10% and 20%of distance between specified points on scalp.

• Lateral Measurement(21 electrode system) The distance is measured from left to right points.

Bl k Di f EEG R d



Block Diagram of EEG Recorder:

Montages:

A pattern of electrode on the head and the channels

they are connected is called montage.Electrode Montage Selector:

It is a large panel containing switches and makearray of channel output.

Each channel is created in the form of input from–

Preamplifier:



Preamplifier:

Every channel has an individual, multistage, accoupled and sensitive amplifier.

The amplifier should have high gain and low noisecharacteristics because EEG potential are small inamplitude.

Noise plays an crucial role hence skin electrodecouple brain waves of only a few microvolt to theamplifier. Hence specially designed connector boxcan be mounted near the patient.

Sensitivity control:

The overall gain of EEG machine is the gain of the

amplifier multiplied by the sensitivity of the writer.

If the writer sensitivity is 1cm/V then amplifiershould have 20,000 gain for 50uV signal.

Artifacts cause excessive deflection to pen. To

overcome this problem most of modern EEG



Filter:

Due to scalp movement & neck movement thenoise would generate.

The most effective way to eliminate this artifactfilter is used. The filters areLow pass filter(frequencies like 0.16,0.53,1.6,5.3).

High pass filter(frequencies like 15,30,70 & 300).

Notch filter(It turns ON sharply at 50hz hence toeliminate mains frequency interface).

Writing Part:

Ink type direct writing recorder havingfrequency response of about 90Hz.

Ink jet recording system gives response up to1000Hz.

Paper drive:



ape d e

It is provided by synchronous motor.

It has paper speed selection as speed of 15,30,60m/s.

Channels:

An EEG is recorded simultaneously from an array of many electrode. Record can be made from Bipolaror monopolar leads.

Commercial EEG machine have up to 32 channeland although 8 or 16 channel are more common.Microprocessor are now employed in EEG machines.

EEG Recording modes:

Unipolar (potential can be measured with referenceto one electrode)

Average Mode: (between 1 electrode and avg of allother electrode)

Bipolar mode: (between sucessive pair of electrode



Analysis of EEG waveform:



Application of EEG:

Epilepsy.

Anesthetic level.

Brain injury.

Monitor during surgery.

Effect of yoga.

EMG(electro myograph)It is an instrument used to record the electrical

activity of muscle to determine whether muscle iscontracting or not.

Study of neuromuscular function is possible byusing EMG.

Muscular contraction are caused by thedepolarization of muscle fibres.

EMG di t



EMG recording system:

EMG potentials are taken from the tissue byelectrode.

Potentials are given to differential amplifier(highgain amp). Its frequency range is 10Hz to10KHz.

Bandwidth of EMG is large and CMRR of this diff

amp i2 80 to 100db.

There is no lead selector switch. Because only 2



yelectrodes are used.

Output from diff amp is given to loudspeakersystem, tape recorder and CRO.

Before giving output to the loud speaker, it is givento the power amplifier. Power amplifier amplifies thesignal given to it.

The output is displayed using CRO. Here storage

oscilloscope is used. And recorded by using taperecorder for future purpose.

Conduction Velocity measurement:

In modern EMG system, nerve conduction time and

nerve velocity are measured. For this measurementinitially nerve is stimulated, and EMG is measured.

Steps Involved in measurement of conductionVelocity:

Stimulate is applied at point AElectrical activit of muscle is measured at oint B.



Now change the position of A into C. Now the space isreduce it is noted as l2 meters.

The time delay is noted as t2 second.

The conduction velocity V=(l1-l2)/(t1-t2)

Usually V=50m/sec, if it is <40m/sec it means somedisorder in nerve conduction.

Application of EMGElectrophysiological testing

Clinical neurophysiology

Neurology

ERG



ERG:

It is the method of recording and interpreting theelectrical activity of the eye.The process of

recording the potential when light falls on the eyeis known as electro retinography.

In ERG, bipolar recording technique is used.

The exploring electrode is placed on a saline filled

contact lens. The contact lens in fixed on an eye.

Negative pressure technique is used to attachcontact lens on an eye.so even during eyemovement, contact lens is not removed.

Normally used contact lens are not used forrecording ERG.

Special type of contact lens is used to record theaction potential of eye when flash of light incidenton eye.

EOG



EOG:

EOG is the recording of the biopotentials generatedby the movement of eyes.

The electrodes are placed to measure horizontal andvertical movement.

The signals from these electrode are given to theamplifier circuit.

Effect of some drugs on the eye movement system scan be identified.

The level of anesthesia can be indicated bycharacteristic of eye movement. Diagnosis of

neurologic disorder are possible.



If flash light on the eye for 2 sec, then some

waveform is generated in the output unitWhen the flash of light incident on eye, the wave

starts from the point a, it is due to Early ReceptorPotential(ERP).

Second component b is due to late receptor (LRP)produced by the synaptic ending of thephotoreceptors. At pt b max o/p is otained.

C wave-offset of light stimulus.

D wave- off response of ERP and LRP

PCG(phono cardiogram)



The graphical record of heart sound is called phonocardiogram.

The device which used to measure heart sound

called phonocariograph. The technique of listening sound produced by

organs and vessels of the body known asAusculation.

The different types of heart sound are measured. These heart sounds are due to the vibration set upin the blood inside the heart by sudden closure of valves.

Murmurs are generally caused by improper openingof the valves.

Cl ifi ti f h t d



Classification of heart sound:

Valve closure sound, ventricular filling sound, valveopening sound, Extra cardiac sound.

Patient monitoring & intensive



Patient monitoring & intensivecare system The system involves continuous measurement of physiology

parameters like respiratory rate, body temperature, bloodpressure, heart rate. In some situation EEG,ECG,EMG aremonitored.

The use of continuous monitoring can be significantly improvethe attention given by hospital staff to a patient in the most

critical condition.

R i t f ti t it i t



Requirement of patient monitoring system:

For any desired parameter, continous monitoringshould be possible.

An alarm should be provided so that if particularparameter changes beyond the limit, then thedoctor or nurse will be informed.

For respiration rate, instead of spirometer type

equipment a thermistor placed near the nasalopening is used, when the patient breath out, thevariation resistance can give an indication of therespiratory rate.

System Arrangement of an ICU:

Bedside monitors consisting of individual unit withwall mount or mobile stands are used.

Monitoring equipment information should displayedat nurse station.

Patient monitorin s stem var in size and

In ad ance s stem central station is pro ided ith



In advance system central station is provided withdata recording provided with data recording taperecorder.

It is recorded in digital form and given tocomparator to sense the level of the signal and thento alarm.

Time delay is given [due to artifacts only when longperiod abnormal data received then alarm isoperated].

Data transmission System in ICU:

In ICU transmission part is very important. Thereare four mode of transmission is occurs as,Wire connection and radio link.

Magnetic tape recorder and commercial telephone line.

• Wire and radio link are most used technique and they aresimple and low cost. Their installation is complex.

• Radio links are useful where the ICU is installed in a



Transmitter used usually have a range of 100m andfrequency must be according to permission withgovernment authority.

Radio link system has poor performance under

certain atmospheric condition.

Magnetic tape recorder is used for permanentrecord.

LAN, Integrated service Digital network(ISDN) and

communication system are useful in patient

Resuscitation Unit:



Resuscitation Unit:

It is must for every ICU. In modern hospital it is inform of mobile trolley.

Equipment mounted areDual trace oscilloscope for ECG, pulse monitoring

Heart rate monitor, graphic recorder, DC defibrillator

Pacemaker

Direct arterial or venous pressure monitoring with



Direct arterial or venous pressure monitoring withmeter may be included.

Special attention should be given to makeinstrument as compact. Hence operator will notmake mistake.

Resuscitation unit may have power pack of 70ampere/hour, storage battery, inverter and batterycharger.

Switch gear and relay are provided when trolley ismoved it changes to self contained power.

Documents

Medical Electronics 1